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Argill is that part of clay to which this owesits property of feeling soft and unctuous, andof hardening in fire; it is difficultly soluble inacids, and scarce ever effervesces with them.When combined with the vitriolic acid, it formsalum.

Silicious Earth is often found in a stony form,such as flint or quartz; and still more frequentlyin that of a very fine sand, such as that whereofglass is made. It does not effervesce, nor is itsoluble in any of the common acids.

To these we may add Iron , in that imperfectstate in which it exists when reduced to rust,and commonly called Calx of Iron.

The soils most frequently met with, andwhich deserve a distinct consideration, are clay,chalk, sand, and gravel, clayey loam, chalkyloam, sandy loam, gravelly loam, ferruginousloam, boggy soil, and heathy soil, or mountain,as it is often called.

Clay is of various colours; for we meet withwhite, grey, brownish red, brownish black, yel-low or bluish clays; it feels smooth, and some-what unctuous: if moist, it adheres to thefingers, and if sufficiently so, it becomes tough